There is a growing understanding of the need to provide individual workspace environmental control in modern office buildings. For example, some studies have suggested a link between an office worker's sense of comfort and well-being and his/her productivity. Research has also shown that there is variation within any population of people and tasks being formed as to what constitutes thermal and visual comfort. By "thermal comfort" we mean an individual's perception that their immediate surrounding is not too hot or too cold. Similarly, "visual comfort" can be used to describe an ambient lighting level that the user perceives as adequate for the task at hand. Historically, temperature is controlled by a wall thermostat for a floor or zone of a building. Lighting conventionally is controlled by rheostats or light switches that control specific lights or banks of lights. In both cases, the prior art control mechanisms do not adequately serve the individual worker's comfort needs, especially in open office areas.
Variable air volume (VAV) systems have been employed for heating and air conditioning in commercial buildings for some years. They are currently the system of choice by the industry, and widely used in office and institutional buildings. In a variable air volume system, one or more central air supply systems are sized to meet the peak cooling (and/or heating) conditions for the building. Several "terminal units" or "boxes" are located in respective zones or offices throughout the building, each connected via ducts to the central air supply. Each terminal unit is sized to meet peak conditions of the space it serves which may or may not coincide with the building's peak conditions. Each terminal unit in a variable volume air system is provided with a preset box maximum airflow. The unit reacts to meet the loads on the corresponding space (or "zone") as determined by a space temperature sensor, and provides airflow to cool (or heat) the space up to that preset maximum airflow. No further airflow will be delivered no matter how much further the space temperature varies from predetermined setpoint conditions. Thus, the prior art terminal unit maximum airflow constrains the unit to ensure that a reasonable balance of airflow is available to all units and all times, even when some zones may be experiencing severe or unusual loads. Moreover, considerable time and expense is required to "balance" variable airflow systems at the time of their installation to achieve the desired distribution of air, and manufacturers typically recommend rebalancing every few years as the loads in each zone change.
An example of a variable air volume ventilating system is shown in U.S. Pat. No. 5,005,636. Variable air volume terminal units are shown in U.S. Pat. No. 4,942,921 to Haessig et al. In general, the prior art terminal units respond to zone temperature (and temperature setpoints), without taking into account other conditions within the zone or in other zones. Moreover, prior art terminal units respond to temperature changes solely by varying airflow volume and/or mix of conditioned and return air. They make no attempt to take into account or to influence other conditions, such as lighting level or airflow direction, that affect user comfort together with zone temperature.